How to initializing std::set correctly?

How to initializing std::set correctly?

Please help me, I have been trying to do this for the past two-three
hours, all with no luck. I have a number of strings comming in form
input.txt in the format
string1 string2
string3 string4
etc.
that I want to put into a std::set which is initially empty. I want to
number the strings as they come in and put them into the set to keep track
of the duplicates so I don't number them again. I am trying to initialize
std::set<std::string> inGraph but can't make it work. I tried to
initialize std::set<std::string> inGraph(0, tot_lines); where 0 to
tot_lines is the range of the number of total strings I expect to get form
the input. The I tried to initialize all with empty stirng like:
std::set<std::string> inGraph(tot_lines, ""); and that failed. Here's what
I have now:
struct StringInt {
std::string name; // associate name and number for each input string
int number;
};
int main(int argc, char* argv[]) {
int tot_lines = 100;
int icv1, icv2;
std::string vert1, vert2;
std::set<std::string> inGraph(); // this is the set I want to initialize
std::set<std::string>::iterator sit;
std::vector<StringInt> stringInts(tot_lines*2);
StringInt* si;
std::ifstream myfile2 ("input.txt");
if (myfile2.is_open()) {
while(myfile2 >> vert1 >> vert2) {
// read in input, put it in vars below
myfile2 >> vert1 >> vert2;
if (inGraph.find(vert1) != inGraph.end()) {
icv1 = i++;
si->name = vert1;
si->number = icv1;
inGraph.insert(vert1);
stringInts.push_back(*si);
}
else {
icv1 = si->number;
}
if (inGraph.find(vert2) != inGraph.end()) {
icv2 = i++;
si->name = vert1;
si->number = icv2;
inGraph.insert(vert2);
stringInts.push_back(*si);
}
else {
icv2 = si->number;
}
}
The error I get is: left of '.find' must have class/struct/union Can you
please help me figure out how to initialize the std::set<std::string>
inGraph so I can number the strings?